DE102015104468B4 - METHOD OF ESTIMATING ROAD SLOPE BASED ON OUTPUT OF A LONG-LINE ACCELERATION SENSOR IN A VEHICLE - Google Patents

Abstract

A method that includes:
a longitudinal acceleration of a vehicle (400) is estimated based on a transmission output speed and/or a wheel speed;
the longitudinal acceleration of the vehicle (400) is measured;
an offset in the measured longitudinal acceleration is determined;
estimating a grade of a road on which the vehicle (400) is traveling based on the estimated longitudinal acceleration, the measured longitudinal acceleration, and the offset; and
an actuator (102) of the vehicle (400) is controlled based on the estimated road grade; characterized in that
the offset is determined based on a first road grade estimated when the vehicle (400) is parked at a location while pointing in a first direction and a second road grade estimated when the vehicle (400) is on is parked in the same location and facing in a second direction that is opposite to the first direction.

Description

AREA

The present invention relates to internal combustion engines and more particularly to a method according to the preamble of claim 1 for estimating road gradient based on an output of a longitudinal acceleration sensor in a vehicle, of the kind essentially known from US Pat DE 10 2007 012 829 A1 is known. Processes that are essentially comparable in type are disclosed in the publications DE 102 48 432 A1 and DE 10 2009 026 688 A1 out.
With regard to the further state of the art, please refer to the publications at this point DE 102 05 971 A1 and U.S. 2007/0 067 137 A1 referred.

BACKGROUND

Some powertrain control systems estimate the grade of a road on which a vehicle is traveling and control an engine and transmission based on the estimated road grade. For example, under normal conditions, a powertrain control system may automatically stop the engine when the engine is idling and automatically restart the engine when a brake pedal is released or an accelerator pedal is applied. However, if the estimated road grade is greater than a predetermined grade, indicating that the vehicle is on a steep hill, the powertrain control system may refrain from automatically stopping the machine.

In another example, the powertrain control system may adjust a transmission shift pattern based on the estimated road grade.

geschätzt, wobei α die Straßenneigung ist, F_g die Kraft ist, die aufgrund der Schwerkraft auf das Fahrzeug wirkt, F_α die Kraft ist, die aufgrund der Straßenneigung auf das Fahrzeug wirkt, m die Masse des Fahrzeugs ist und a_g die Beschleunigung des Fahrzeugs aufgrund der Schwerkraft ist. Die Masse des Fahrzeugs kann auf der Grundlage einer angenommenen Anzahl von Fahrgästen und eines angenommenen Ladegewichts vorbestimmt werden. Die Beschleunigung des Fahrzeugs aufgrund der Schwerkraft kann ein vorbestimmter Wert sein (z.B. 9,8 Meter pro Sekunde im Quadrat).Road grade is typically calculated using a relationship such as $$\text{sin}a\text{=}\frac{f_G}{f_a}=\frac{m{a}_G}{f_a}$$

where α is the road gradient, F _g is the force acting on the vehicle due to gravity, F _α is the force acting on the vehicle due to road gradient, m is the mass of the vehicle, and a _g is the acceleration of the vehicle due to gravity. The mass of the vehicle may be predetermined based on an assumed number of passengers and an assumed payload. The acceleration of the vehicle due to gravity may be a predetermined value (eg, 9.8 meters per second squared).

geschätzt, wobei ΣF eine Summe der Längskräfte ist, die auf das Fahrzeug wirken, FENG die Kraft ist, die aufgrund des Drehmomentausgangs der Maschine auf das Fahrzeug wirkt, FAD die aerodynamische Kraft ist, die auf das Fahrzeug wirkt, F_α die Kraft ist, die aufgrund der Straßenneigung auf das Fahrzeug wirkt, m die Masse des Fahrzeugs ist und a_L die Längsbeschleunigung des Fahrzeugs ist. Die Kraft, die aufgrund des Drehmomentausgangs der Maschine auf das Fahrzeug wirkt, kann auf der Grundlage von gemessenen Maschinenbetriebsbedingungen geschätzt werden. Die aerodynamische Kraft, die auf das Fahrzeug wirkt, kann auf der Grundlage einer angenommenen Windkraft geschätzt werden. Die Längsbeschleunigung des Fahrzeugs kann auf der Grundlage einer gemessenen Fahrzeuggeschwindigkeit ermittelt werden.The force acting on a vehicle due to road grade is typically calculated using a relationship such as $${\displaystyle \sum \text{f}={\text{f}}_{\text{CLOSELY}}+{\text{f}}_{\text{AD}}}+{\text{f}}_{\mathrm{a}}={\text{mom}}_{\text{L}}$$

where ΣF is a sum of the longitudinal forces acting on the vehicle, FENG is the force acting on the vehicle due to engine torque output, FAD is the aerodynamic force acting on the vehicle, F _α is the force, acting on the vehicle due to road gradient, m is the mass of the vehicle, and a _L is the longitudinal acceleration of the vehicle. The force acting on the vehicle due to engine torque output may be estimated based on measured engine operating conditions. The aerodynamic force acting on the vehicle can be estimated based on an assumed wind force. The longitudinal acceleration of the vehicle can be determined based on a measured vehicle speed.

Powertrain control systems typically assume that a vehicle is moving when estimating the torque output of an engine in the vehicle based on engine operating conditions. Furthermore, the relationship typically used to estimate the force acting on a vehicle due to road grade does not take into account the force acting on the vehicle due to braking. Thus, when a vehicle is stopped or when a brake is applied, powertrain control systems typically do not estimate road grade due to possible inaccuracies in the estimated road grade. Furthermore, even if the vehicle is moving and the brake is not applied, the estimated road grade may be inaccurate due to other assumptions made in estimating the road grade. These other assumptions may include assumed number of passengers, assumed cargo weight, and/or assumed wind power.

Inaccuracies in the estimated road grade can adversely affect a powertrain control system's ability to control an engine and transmission based on the estimated road grade. For example, the estimated road grade may incorrectly indicate that a vehicle is on a steep hill. Therefore, the powertrain control system may not automatically stop an engine when the engine is idling is located as desired, which can adversely affect fuel economy.

SUMMARY

According to the invention, a method for estimating the road gradient is proposed, which is characterized by the features of claim 1.

A system is also described that includes a longitudinal acceleration estimation module, a vehicle longitudinal acceleration sensor, a road grade estimation module, and an actuator control module. The longitudinal acceleration estimation module estimates a longitudinal acceleration of a vehicle based on a transmission output speed and/or a wheel speed. The vehicle longitudinal acceleration sensor measures the longitudinal acceleration of the vehicle. The road grade estimation module estimates a grade of a road on which the vehicle is traveling based on the estimated longitudinal acceleration and the measured longitudinal acceleration. The actuator control module controls an actuator of the vehicle based on the estimated road grade.

Further areas of applicability of the present invention will become apparent from the detailed description, claims, and drawings. The detailed description and specific examples are intended for purposes of explanation only.

character list

• 1 ein Funktionsblockdiagramm eines beispielhaften Maschinensystems gemäß den Prinzipien der vorliegenden Erfindung ist;
• 2 ein Funktionsblockdiagramm eines beispielhaften Steuersystems gemäß den Prinzipien der vorliegenden Erfindung ist;
• 3A und 3B Graphen, die ein beispielhaftes Verfahren zum Ermitteln eines Offsets bei einem Ausgang eines Fahrzeuglängsbeschleunigungssensors darstellen, gemäß den Prinzipien der vorliegenden Erfindung sind;
• 4 ein Funktionsblockdiagramm, das ein beispielhaftes Verfahren zum Ermitteln eines Offsets bei einem Ausgang eines Fahrzeuglängsbeschleunigungssensors darstellt, gemäß den Prinzipien der vorliegenden Erfindung ist;
• 5 ein Flussdiagramm, das ein beispielhaftes Verfahren zum Schätzen einer Straßenneigung auf der Grundlage eines Ausgangs eines Fahrzeuglängsbeschleunigungssensors darstellt, gemäß den Prinzipien der vorliegenden Erfindung ist; und
• 6 bis 11 Flussdiagramme, die beispielhafte Verfahren zum Ermitteln eines Offsets bei einem Ausgang eines Fahrzeuglängsbeschleunigungssensors darstellen, gemäß den Prinzipien der vorliegenden Erfindung sind.

The present invention will be more clearly understood from the detailed description and the accompanying drawings, wherein:

• 1 Figure 12 is a functional block diagram of an exemplary engine system according to the principles of the present invention;
• 2 Figure 12 is a functional block diagram of an exemplary control system according to the principles of the present invention;
• 3A and 3B 10 are graphs illustrating an exemplary method for determining an offset in an output of a vehicle longitudinal acceleration sensor, according to the principles of the present invention;
• 4 Figure 12 is a functional block diagram illustrating an exemplary method for determining an offset in an output of a vehicle longitudinal acceleration sensor, according to the principles of the present invention;
• 5 13 is a flow chart illustrating an exemplary method for estimating a road grade based on an output of a vehicle longitudinal acceleration sensor, according to the principles of the present invention; and
• 6 until 11 Flow charts depicting example methods for determining an offset in an output of a vehicle longitudinal acceleration sensor are according to the principles of the present invention.

Reference numbers may be reused in the drawings to identify similar and/or identical items.

DETAILED DESCRIPTION

A method according to the present invention avoids inaccuracies in road grade due to the assumptions described above by estimating road grade based on input from a vehicle longitudinal acceleration sensor. Thus, the system and method can accurately estimate the road grade even when the vehicle is stopped or a brake is applied. In addition, the system and method further improves the accuracy of the estimated road grade by accounting for offsets in the vehicle longitudinal acceleration sensor output. The offsets may be due to sensor placement, a change in cargo weight due to a different number of passengers and/or adding a trailer, and/or a variation in sensor output over the life of the vehicle.

Now on 1 Referring now, an example implementation of a vehicle system 100 includes an engine 102 that combusts an air/fuel mixture to produce drive torque for a vehicle. The amount of drive torque produced by the engine 102 is based on the position of an accelerator pedal 104. The amount of drive torque produced by the engine 102 may also be based on a cruise control system, which may be an adaptive cruise control system that changes vehicle speed by a predetermined one to maintain following distance.

Air is drawn into the engine 102 via an intake system 108 . For example only, the intake system 108 may include an intake manifold 110 and a throttle 112 . For example only, the throttle 112 may comprise a butterfly valve having a rotatable vane. An engine control module (ECM) 114 controls a throttle actuator module 116 that regulates the opening of the throttle plate 112 to control the amount of air drawn into the intake manifold 110 .

The air from the intake manifold 110 is drawn into the cylinders of the engine 102 . While engine 102 may include multiple cylinders, only a single representative cylinder 118 is shown for purposes of explanation. For example only, engine 102 may include 2, 3, 4, 5, 6, 8, 10, and/or 12 cylinders. The ECM 114 may deactivate a portion of the cylinders, which may improve fuel economy under certain engine operating conditions.

The ECM 114 may start and stop the engine 102 based on input received from an ignition system 119 . The ignition system 119 may include a key or a button. The ECM 114 may start the engine 102 when a driver turns the key from an off position to an on (or drive) position or when the driver presses the button. The ECM 114 may stop the engine 102 when an operator turns the key from the on position to the off position or when the operator presses the button while the engine 102 is running.

The engine 102 may operate using a four stroke cycle. The four strokes described below may be referred to as the intake stroke, compression stroke, power stroke, and exhaust stroke. During each revolution of a crankshaft 120, two of the four strokes in the cylinder 118 occur. Therefore, it takes two crankshaft revolutions for cylinder 118 to experience all four strokes.

During the intake stroke, air is drawn from the intake manifold 110 into the cylinder 118 via an intake valve 122 . The ECM 114 controls a fuel actuator module 124 that regulates fuel injection to achieve a target air/fuel ratio. Fuel may be injected into the intake manifold 110 at a central location or at multiple locations, such as near the intake valve 122 of each of the cylinders. In various implementations, the fuel may be injected directly into the cylinders or into mixing chambers associated with the cylinders. The fuel actuator module 124 may stop injecting fuel into cylinders that are deactivated.

The injected fuel mixes with the air and creates an air/fuel mixture in the cylinder 118. During the compression stroke, a piston (not shown) in the cylinder 118 compresses the air/fuel mixture. The engine 102 may be a compression ignition engine, in which case compression in the cylinder 118 ignites the air/fuel mixture. Alternatively, the engine 102 may be a spark-ignition engine, in which case a spark actuator module 126 energizes a spark plug 128 to generate an ignition spark in the cylinder 118 based on a signal from the ECM 114 that affects the air/fuel mixture ignites. The timing of the spark can be specified relative to when the piston is at its topmost position, referred to as top dead center (TDC).

The spark actuator module 126 may be controlled by a spark timing signal that indicates how far before or after TDC to spark. Since piston position is directly related to crankshaft rotation, operation of the spark actuator module 126 can be synchronized to crankshaft angle. In various implementations, the spark actuator module 126 may stop providing spark for deactivated cylinders.

The generation of the ignition spark can be referred to as an ignition event. The spark actuator module 126 may have the capability to change the timing of the spark for each spark event. The spark actuator module 126 may even change spark timing for a next spark event if the spark timing signal is changed between a last spark event and the next spark event. In various implementations, the engine 102 may include multiple cylinders and the spark actuator module 126 may change spark timing relative to TDC for all cylinders in the engine 102 by the same amount.

During the power stroke, combustion of the air/fuel mixture drives the piston down, thereby driving crankshaft 120 . Power stroke can be defined as the time between when the piston reaches TDC and when the piston returns to bottom dead center (BDC). During the exhaust stroke, the piston begins to move up from BDC and forces the by-products of combustion out through an exhaust valve 130 . The by-products of the combustion escape the vehicle via an exhaust system 134 .

Intake valve 122 may be controlled by an intake camshaft 140 while exhaust valve 130 may be controlled by an exhaust camshaft 142 . In various implementations, multiple intake camshafts (comprising intake camshaft 140) may control multiple intake valves (comprising intake valve 122) for cylinder 118 and/or may control intake valves (comprising intake valve 122) of multiple banks of cylinders (comprising cylinder 118 include) control. In a similar way may control multiple exhaust camshafts (including exhaust camshaft 142) multiple exhaust valves for cylinder 118 and/or may control exhaust valves (including exhaust valve 130) for multiple banks of cylinders (including cylinder 118).

The timing at which the intake valve 122 opens may be altered with respect to piston TDC by an intake cam phaser 148 . The timing at which the exhaust valve 130 opens may be altered with respect to piston TDC by an exhaust cam phaser 150 . A valve actuator module 158 may control the intake and exhaust cam phasers 148, 150 based on signals from the ECM 114. In one implementation, variable valve lift may also be controlled by valve actuator module 158 .

The valve actuator module 158 may deactivate the cylinder 118 by inhibiting opening of the intake valve 122 and/or the exhaust valve 130 . The valve actuator module 158 may inhibit opening of the intake valve 122 by decoupling the intake valve 122 from the intake cam phaser 148 . Similarly, the valve actuator module 158 may inhibit opening of the exhaust valve 130 by decoupling the exhaust valve 130 from the exhaust cam phaser 150 . In various implementations, the valve actuator module 158 may control the intake valve 122 and/or the exhaust valve 130 using devices other than camshafts, such as electromagnetic or electrohydraulic actuators.

Torque output at the crankshaft 120 is transmitted to wheels 162 via a drive system 160 . In the exemplary realization of the in 1 In the engine system 100 shown, the powertrain system 160 includes a torque converter 164, a transmission 166, a driveshaft 168, a transaxle 170, and axleshafts 172. In other implementations, the powertrain system 160 may not include one or more of these components. The torque converter 164 , transmission 166 , and transaxle 170 augment engine torque through various gear ratios to provide axle torque at the axleshafts 172 . The axle torque rotates the wheels 162, thereby accelerating the vehicle. The driver can reduce the speed of the vehicle by depressing a brake pedal 174 .

The vehicle system 100 may measure the position of the accelerator pedal 104 using an accelerator pedal position sensor (APP) sensors 176 . The position of the brake pedal 174 may be measured using a brake pedal position sensor (BPP) 178 . The position of the crankshaft 120 may be measured using a crankshaft position sensor (CKP) 180 . The engine coolant temperature may be measured using an engine coolant temperature sensor (ECT) sensor 182 . The ECT sensor 182 may be located within the engine 102 or other locations where coolant circulates, such as a radiator (not shown).

The pressure in the intake manifold 110 may be measured using a manifold absolute pressure sensor (MAP) sensor 184 . In various implementations, an engine vacuum comprising the difference between ambient air pressure and the pressure within the intake manifold 110 may be measured. The mass air flow rate of the air flowing into the intake manifold 110 may be measured using a mass air flow (MAF) sensor 186 . In various implementations, the MAF sensor 186 may be in a housing that also includes the throttle body 112 .

The throttle actuator module 116 may monitor the position of the throttle 112 using one or more throttle position sensors (TPS) 188 . The ambient temperature of the air drawn into the engine 102 may be measured using an intake air temperature (IAT) sensor 190 . The ambient pressure of the air may be measured using an intake air temperature sensor (AAP) 191 . The output speed of the transmission 166 may be measured using a transmission output speed (TOS) sensor 192 . The speed of the wheels 162 may be measured using a wheel speed sensor (WSS) 194 .

Longitudinal acceleration of the vehicle may be measured using a vehicle longitudinal acceleration sensor (VLA) 196 . The VLA sensor 196 may be attached to a body and/or frame of the vehicle. In various implementations, the VLA sensor 196 may also measure the vehicle's lateral acceleration and the vehicle's yaw rate. The ECM 114 can use signals from the sensors to make control decisions for the vehicle system 100 .

The ECM 114 may communicate with a transmission control module (TCM) 198 to coordinate shifting of gears in the transmission 166 . For example, the ECM 114 may reduce engine torque during a gear shift. Although some of the sensor signals are shown as being provided to the TCM 198 , the TCM 198 may forward those sensor signals to the ECM 114 . Alternatively, these sensor signals can be provided to the ECM 114 directly. In various implementations, various ECM 114 and TCM 198 functions may be integrated into one or more modules. Even though 2 While FIG. Further, the ECM 114, the TCM 198, and/or sensors that provide signals to the ECM 114 and/or the TCM 198 may collectively be referred to as a powertrain control system.

Now on 2 Referring to this, an example implementation of the ECM 114 includes a longitudinal acceleration estimation module 202. The longitudinal acceleration estimation module 202 estimates the vehicle's longitudinal acceleration based on the transmission output speed from the TOS sensor 192. For example, the longitudinal acceleration estimation module 202 may estimate the vehicle's speed based on the Determine the basis of the transmission output speed and determine the derivative of the vehicle speed with respect to time to obtain the longitudinal acceleration. The longitudinal acceleration estimation module 202 may estimate the longitudinal acceleration based on wheel speed from the WSS 194 in a similar manner.

schätzen, wobei (a_L)_α die Längsbeschleunigung aufgrund der Straßenneigung ist, (aL)MEAs die gemessene Längsbeschleunigung ist, (a_L)_EST die geschätzte Längsbeschleunigung ist und (a_L)_OFF eine Längsbeschleunigung aufgrund eines Offsets bei dem Ausgang des VLA-Sensors 196 ist.A road grade estimation module 204 estimates the grade of the road the vehicle is traveling on based on the estimated longitudinal acceleration and the longitudinal acceleration measured by the VLA sensor 196 . For example, the road grade estimation module 204 may determine a longitudinal acceleration due to the road grade based on the estimated and measured longitudinal acceleration and estimate the road grade based on the longitudinal acceleration due to the road grade. The road grade estimation module 204 may estimate the longitudinal acceleration due to the road grade using a relationship such as $${\left({\text{a}}_{\text{L}}\right)}_{\mathrm{a}}={\left({\text{a}}_{\text{L}}\right)}_{\text{MEAS}}-{\left({\text{a}}_{\text{L}}\right)}_{\text{EST}}-{\left({\text{a}}_{\text{L}}\right)}_{\text{OFF}}$$

where (a _L ) _α is longitudinal acceleration due to road grade, (aL)MEAs is measured longitudinal acceleration, (a _L ) _EST is estimated longitudinal acceleration, and (a _L ) _OFF is longitudinal acceleration due to an offset in the output of the VLA Sensor 196 is.

schätzen, wobei α die Straßenneigung ist, F_g die Kraft ist, die auf das Fahrzeug aufgrund der Schwerkraft wirkt, F_α die Kraft ist, die auf das Fahrzeug aufgrund der Straßenneigung wirkt, m die Masse des Fahrzeugs ist und a_g die Beschleunigung des Fahrzeugs aufgrund der Schwerkraft ist und (a_L)_α die Längsbeschleunigung aufgrund der Straßenneigung ist. Die Masse des Fahrzeugs und die Beschleunigung des Fahrzeugs aufgrund der Schwerkraft können vorbestimmt sein.The road grade estimation module 204 may estimate the road grade based on the longitudinal acceleration due to the road grade using a relationship such as $$\text{sin}a\text{=}\frac{f_G}{f_a}=\frac{m{a}_G}{m{\left(a_L\right)}_{\propto }}=\frac{a_G}{{\left(a_L\right)}_{\propto }}$$

where α is the road gradient, F _g is the force acting on the vehicle due to gravity, F _α is the force acting on the vehicle due to road gradient, m is the mass of the vehicle, and a _g is the acceleration of the vehicle due to gravity and (a _L ) _α is the longitudinal acceleration due to road grade. The mass of the vehicle and the acceleration of the vehicle due to gravity may be predetermined.

A sensor offset determination module 206 determines the offset in the output of the VLA sensor 196. The sensor offset determination module 206 may determine the sensor offset using a number of different methods, the duration of which varies. For example, some methods determine sensor offset almost instantaneously, while other methods determine sensor offset over a short period of time (e.g., days or weeks). Still other methods determine the sensor offset over a medium to long term (e.g. one month to the life of the vehicle).

The sensor offset determination module 206 may use an immediate method to determine the sensor offset when the vehicle is first assembled. In this method, the vehicle is parked on an area with a predetermined incline (eg, 0%). A user then communicates with the ECM 114 using, for example, a user interface device (eg, a touchscreen) in the vehicle or an external module (eg, a scanning tool) to provide the sensor offset determination module 206 with the predetermined slope. The sensor offset determination module 206 determines the sensor offset based on input from the VLA sensor 196 and the predetermined tilt. For example, the sensor offset determination module 206 may estimate a longitudinal acceleration based on the predetermined grade and set the sensor offset equal to the difference between the measured and estimated longitudinal acceleration. The sensor offset determination module 206 may permanently store the sensor offset in non-volatile memory and the sensor offset over the lifetime of the vehicle adjust based on sensor offsets determined using other methods.

The sensor offset determination module 206 may adjust the sensor offset by a percentage of a newly determined sensor offset based on the method used to determine the new sensor offset. For example, the sensor offset determination module 206 may adjust the sensor offset by a large percentage (e.g., 100 percent (%)) of a new sensor offset when the new sensor offset is determined using an immediate method. The sensor offset determination module 206 may adjust the sensor offset by an average percentage (e.g., 30% to 40%) of a new sensor offset when the new sensor offset is determined using a short runtime method. The sensor offset determination module 206 may adjust the sensor offset by a small percentage (e.g., 0% to 10%) of a new sensor offset when the new sensor offset is determined using a medium to long term method.

The sensor offset determination module 206 may use another immediate method to determine the sensor offset each time the ignition key is turned off (e.g., each time the ignition system 119 is cycled from on to off). In this method, each time the ignition key is turned off, the sensor offset determination module 206 stores the last reading from the VLA sensor 196 before the ignition key was turned off. Then, the next time the ignition key is turned on (e.g., the next time the ignition system 119 is switched from off to on), the sensor offset determination module 206 receives a new reading from the VLA sensor 196. The sensor offset determination module 206 then determines the sensor offset based on the stored reading and the new reading. For example, the sensor offset determination module 206 may assume the vehicle is in the same location when the ignition key is turned off and when the ignition key is turned on, and set the sensor offset equal to the difference between the stored reading and the new reading.

Thus, if the pitch angle of the vehicle changes due to, for example, a change in the number of passengers or a trailer being attached to the vehicle during key-off, the sensor offset reflects the change in vehicle pitch angle. A similar method can be used to determine the sensor offset as the vehicle pitch angle changes without turning off the ignition system 119 . For example, the sensor offset determination module 206 may store the reading from the VLA sensor 196 after the transmission is shifted into park. The sensor offset determination module 206 may then determine the sensor offset based on differences between the stored reading and new readings from the VLA sensor 196 while the transmission is in park. In various implementations, the sensor offset determination module 206 may determine the sensor offset based on a difference between the stored reading and the last reading from the VLA sensor 196 before the transmission is shifted out of park.

In the method described above, the sensor offset determination module 206 may assume that the vehicle is in the same location for the ignition key off and the ignition key on. Thus, if the vehicle is towed or otherwise moved from one location to another without switching the ignition system 119 from off to on, the sensor offset determined using this method may be inaccurate. Therefore, the road grade estimation module 204 may compare the sensor offset determined during this method to one or more of the sensor offsets using other methods described herein. If the comparison indicates that the sensor offset is unrealistic, the road grade estimation module 204 may not adjust the previous sensor offset based on the newly determined sensor offset.

The sensor offset determination module 206 may use a short runtime method to determine the sensor offset over a relatively short trip (e.g., a 16 to 48 km (10 to 30 miles) trip). In this method, a road grade sum module 208 determines a running sum of road grade estimates. Each road grade estimate may be an average of road grade estimates taken over a predetermined distance (e.g. 1 meter). The sensor offset determination module 206 then determines whether the sum of road grade estimates corresponds to a round trip. If the sum corresponds to a round trip, the sensor offset determination module 206 may adjust the sensor offset based on a difference between the sum and zero and then reset the sum to zero. Otherwise, the sensor offset determination module 206 may reset the sum to zero without adjusting the sensor offset based on the running sum.

The sensor offset determination module 206 may be based on input from a global positioning system (GPS). positioning system), a real-time clock, and/or an ambient temperature sensor to determine if the vehicle has driven back and forth, such as in a daily commute. Ambient temperature can be used as a secondary indicator of time. The sensor offset determination module 206 may determine whether the vehicle has backed up based on periods when the ignition system 119 is off. For example, the sensor offset determination module 206 may determine that the vehicle is home parked when the ignition system 119 is off for at least 10 to 12 hours. The sensor offset determination module 206 may determine that the vehicle is parked at the work site when the ignition system 119 is off for approximately 7 to 9 hours. The sensor offset determination module 206 may determine that the vehicle is parked somewhere other than work or home when the ignition system 119 is off for less than 2 hours.

The sensor offset determination module 206 may determine whether the vehicle has backed out based on a comparison of distances traveled during multiple ignition-on cycles. Each ignition-on cycle may begin when the ignition system 119 is switched from off to on and may end when the ignition system 119 is switched from on to off. The sensor offset determination module 206 may determine that the vehicle has backed up if the distances traveled during two consecutive ignition-on cycles are equal or within a predetermined distance of one another. The sensor offset determination module 206 may determine the distance traveled during each key-on cycle based on wheel speed from the WSS 194 .

The sensor offset determination module 206 may use a medium to long term method to account for sensor offset due to vehicle aging and variation in the output of the VLA sensor 196 over the life of the vehicle. In one such method, a road grade histogram module 210 generates and maintains a histogram 302 of road grade estimates ( 3A) . An x-axis 304 of the histogram 302 represents road grade in percent, and a y-axis 306 of the histogram 302 represents distance traveled in meters. Although the x-axis 304 is shown having a range of -2% to 2% , the x-axis 304 can have a larger range, for example from -50% to 50%. The road grade estimates can be grouped into classes with smaller magnitudes around a grade of about 0% and larger magnitudes at steeper grades. For example, the road grade estimates may be classified into classes such as [-50% -20% -15% -10% -7% -5% -4% -3% -2% -1% -0.75% -0.5% - 0.25% 0% 0.25% 0.5% 0.75% 1% 2% 3% 4% 5% 7% 10% 15% 20% 50%].

The y-axis 306 represents the distance traveled corresponding to each class of road grade estimates, or the percentage of total time traveled for each road grade estimate. The y-axis 306 is positioned at a road grade of 0%. When the sensor offset is zero, the histogram 302 is symmetrical about a road grade of approximately 0%. In other words, the sum of all bins of histogram 302 equals approximately 0%. With this method, the sum of all classes cannot be exactly 0% due to errors.

The sensor offset determination module 206 may adjust the sensor offset based on an amount by which the sum of all classes falls outside of a predetermined range. The sensor offset determination module 206 may adjust the sensor offset at predetermined intervals based on distance traveled (e.g., every 1,600 kilometers (1,000 miles)). Once the sensor offset has been adjusted, the sensor offset determination module 206 may clear all data in the histogram 302 and begin generating a new histogram of road grade estimates.

The predetermined area may be an area centered around a 0% road grade (e.g. +/- 0.278%). The predetermined range may correspond to a worst case error in this method. Worst-case error may correspond to driving the vehicle 19,312 kilometers (12,000 miles) per year from a lowest possible terrain elevation (e.g., -86 meters (-282 feet)) to a highest possible terrain elevation (e.g., 4,401 meters (14,440 feet)).

In various implementations, the data may be presented in a histogram of road grade estimates in the form of a bell-shaped curve 308 ( 3B) being represented. Bell curve 308 is shown with respect to x-axis 304 and y-axis 306 . As with the histogram 302, the bell-shaped curve 308 is symmetrical about a road grade of approximately 0% when the sensor offset is zero. Thus, a difference 310 between a line of symmetry 312 of the bell-shaped curve 308 and the y-axis 306 approximately represents the sensor offset.

ermitteln, wobei ΣEi eine Summe der Höhenänderungen bei einer aktuellen Iteration i ist, ZEi-1 die Summe der Höhenänderungen bei einer vorherigen Iteration i-1 ist, di eine zurückgelegte Distanz, die der aktuellen Iteration i entspricht, ist und αi die geschätzte Straßenneigung für die aktuelle Iteration i ist.In another medium to long term method, an altitude sum module 212 determines changes in the vehicle's altitude based on the estimated road grade and determines a running sum of the altitude changes. The altitude summation module 212 may determine the changes in altitude at predetermined intervals of a distance traveled (eg, every meter). The elevation sum module 212 may sum the elevation changes using a relationship such as $${\displaystyle \sum {\text{E}}_{\text{i}}={\displaystyle \sum {\text{E}}_{\text{i}-1}+{\text{i.e}}_{\text{i}}*\text{sin}\left({\mathrm{a}}_{\text{i}}\right)}}$$

where ΣEi is a sum of elevation changes at a current iteration i, ZEi-1 is the sum of elevation changes at a previous iteration i-1, di is a traveled distance corresponding to the current iteration i, and αi is the estimated road grade for the current iteration is i.

The sensor offset determination module 206 may adjust the sensor offset based on an amount that the sum of the elevation changes is outside of a predetermined range. The sensor offset determination module 206 may adjust the sensor offset at predetermined intervals of distance traveled (e.g., every 1,600 kilometers (1,000 miles)). After adjusting the sensor offset, the sensor offset determination module 206 may reset the sum of elevation changes to zero and determine a new running sum of elevation changes.

The predetermined range may be centered around zero. The predetermined range may correspond to a worst case error in this method. Worst-case error may correspond to driving the vehicle 19,312 kilometers (12,000 miles) per year from a lowest possible terrain elevation (e.g., -86 meters (-282 feet)) to a highest possible terrain elevation (e.g., 4,401 meters (14,440 feet)).

The height of the vehicle can change significantly when the vehicle is being transported from an assembly plant to a dealership. Because vehicles are not typically driven from an assembly plant to a dealership, the sensor offset determined based on the running sum of elevation changes may not be accurate after the vehicle has been transported from the assembly plant to the dealership. Therefore, the running total of elevation changes can be initialized (e.g., zeroed) at the dealer using an external module (e.g., a scanning tool). Alternatively, the altitude sum module 212 may initialize the running sum of altitude changes when the vehicle altitude estimated based on ambient barometric pressure indicates a change in vehicle altitude that is unrelated to driving the vehicle.

The altitude summation module 212 may also determine changes in the altitude of the vehicle based on the ambient barometric pressure from the AAP sensor 191 and determines a running total of the altitude changes. For example, the altitude summation module 212 may estimate the vehicle altitude based on the ambient barometric pressure and determine the altitude changes based on the estimated vehicle altitude. The elevation summation module 212 may determine the elevation changes based on the estimated vehicle height concurrently with the elevation summation module 212 determining the elevation changes based on the estimated road grade.

The sensor offset determination module 206 may compare the sum of the elevation changes determined based on the estimated vehicle height to the sum of the elevation changes determined based on the estimated road grade. The sensor offset determination module 206 may adjust the sensor offset based on the sum of elevation changes determined based on the estimated road grade when the difference between those two sums is within a predetermined range of zero. Otherwise, the sensor offset determination module 206 may not adjust the sensor offset based on the sum of the elevation changes determined based on the estimated road grade.

The elevation sum module 212 may also compare the running total of elevation changes to a lowest possible terrain elevation (e.g., -86 meters (-282 feet)) and a highest possible terrain elevation (e.g., 4,401 meters (14,440 feet)). The elevation sum module 212 may adjust the running total of elevation changes if the running total is less than the lowest possible terrain elevation or greater than the highest possible terrain elevation. For example, if the running total of elevation changes is less than the lowest possible terrain elevation, the elevation totals module 212 may adjust the running total to the lowest possible terrain elevation. Conversely, if the running total is greater than the highest possible terrain elevation, the elevation totals module 212 may adjust the running total to the highest possible terrain elevation.

As discussed above, the sensor offset may be inaccurate when a vehicle is being towed or otherwise moved from a location another is moved without switching the ignition system 119 from off to on. Furthermore, the method used to determine the sensor offset when the vehicle is first assembled may not be performed by vehicle service providers, such as dealers, who do not have access to a surface with a predetermined slope. A different method for determining the sensor offset can thus be used in these cases.

In one such method, the road grade estimation module 204 estimates the road grade when a vehicle 400 ( 4 ) is parked and facing in a first direction. In this circumstance, the VLA sensor 196 measures a first longitudinal acceleration 402 due to the force of gravity 404 acting on the vehicle. Then, the vehicle 400 is rotated 180 degrees and parked in the same location such that the vehicle 400 faces a second direction that is opposite to the first direction. In this circumstance, the VLA sensor 196 measures a second longitudinal acceleration 406 due to gravity 404 acting on the vehicle 400 . The road grade estimation module 204 again estimates the road grade while the vehicle 400 is parked and the sensor offset determination module 206 determines the sensor offset based on the first estimated road grade and the second estimated road grade.

If the first and second estimated road grades have the same sign and approximately the same value, the sensor offset determination module 206 determines that the vehicle 400 is on a flat surface and sets the sensor offset equal to the value of the two estimated road grades. If the first and second estimated road grades have the same sign and different values, the sensor offset determination module 206 determines that a road surface angle 408 is less than a sensor pitch angle 410 . In this case, the sensor offset determination module 206 sets the sign of the sensor offset equal to the sign of the two estimated road grades and sets the magnitude of the sensor offset equal to the difference between the two estimated road grades divided by two.

If the first and second estimated road grades have different signs and different values, the sensor offset determination module 206 determines that the road surface angle 408 is greater than the sensor pitch angle 410 . In this case, the sensor offset determination module 206 sets the sign of the sensor offset equal to the sign of the larger of the two estimated road grades. Further, the sensor offset determination module 206 sets the amount of sensor offset equal to the difference between the two estimated road grades divided by two.

Another method that can be used by vehicle service providers to determine the sensor offset is to clear all data in the histogram of road grade estimates while the vehicle is parked. The vehicle is then driven any distance and returned to the same location and orientation. The sensor offset determination module 206 then sets the sensor offset equal to the difference 310 ( 3B) between the histogram line of symmetry 312 and the 0% slope corresponding to the y-axis 306 .

A start-stop module 214 automatically stops and automatically restarts the engine 102 when the engine 102 is idling. The stop-start module 214 may automatically stop the engine 102 when the vehicle speed is less than or equal to a predetermined speed (e.g., zero) and the driver depresses the brake pedal 174 . The start-stop module 214 may automatically restart the engine 102 when the driver releases the brake pedal 174, when the driver depresses the accelerator pedal 104, and/or when the driver depresses a resume switch (not shown).

The stop-start module 214 may determine the vehicle speed based on the wheel speed from the WSS 194, for example by setting the vehicle speed equal to the wheel speed. The stop-start module 214 may determine when the driver is depressing or releasing the accelerator pedal 104 based on the accelerator pedal position from the APP sensor 176 . The stop-start module 214 may determine when the driver is depressing or releasing the brake pedal 174 based on an input received from the BPP sensor 178 .

The start-stop module 214 may determine whether to automatically stop or restart the machine 102 based on the estimated road grade. For example, the start-stop module 214 may only automatically stop the engine 102 when the engine 102 is idling and the estimated road grade is less than or equal to a predetermined grade, indicating the vehicle is not on a steep hill located. As such, the start-stop module 214 may not automatically stop the engine 102 when the engine 102 is idling if the estimated road grade is greater than the preset true grade, indicating that the vehicle is on a steep hill.

The start-stop module 214 may automatically stop and restart the engine 102 by commanding a throttle control module 216, a fuel control module 218, and/or a spark control module 220 to stop or start the engine 102. The throttle control module 216 may control the throttle 112 by commanding the throttle actuator module 116 to achieve a desired throttle area. The fuel control module 218 may control the delivery of fuel to the cylinder 118 by commanding the fuel actuator module 124 to achieve a desired air/fuel ratio. The spark control module 220 may control the spark plug 128 by commanding the spark actuator module 126 to achieve a desired spark timing.

The throttle control module 216 may stop or restart the engine 102 by commanding the throttle actuator module 116 to fully close or open the throttle 112 . The fuel control module 218 may stop or start the engine 102 by commanding the fuel actuator module 124 to stop or start providing fuel to the cylinder 118 . The spark control module 220 may stop or start the engine 102 by commanding the spark actuator module 126 to stop or start generating a spark.

The TCM 198 may adjust a transmission shift schedule based on the estimated road grade. For example, the TCM 198 may normally shift the transmission based on a predetermined shift schedule. However, if the estimated road grade indicates the vehicle is traveling uphill, the TCM 198 may delay shift points relative to the predetermined shift schedule to generate more torque. The engine 102 and transmission may be referred to as actuators of the vehicle, and the start-stop module 214 and TCM 198 may be referred to as actuator control modules.

Now on 5 Referring now, a method of estimating the slope of a road on which a vehicle is traveling based on an output of a vehicle longitudinal acceleration (VLA) sensor begins at 502. At 504, the method measures the longitudinal acceleration of the vehicle using the VLA sensor. At 506, the method estimates the longitudinal acceleration of the vehicle based on input from a transmission output speed sensor and/or a wheel speed sensor.

At 508, the method determines a longitudinal acceleration due to an offset in the output of the VLA sensor. At 510, the method determines a longitudinal acceleration due to the road grade based on the measured longitudinal acceleration, the estimated longitudinal acceleration, and the longitudinal acceleration due to the sensor offset. For example, the method may determine longitudinal acceleration due to road grade using relationship (3) as discussed above.

At 512, the method estimates road grade based on longitudinal acceleration due to road grade. For example, the method may estimate road grade using relationship (4) discussed above. The procedure ends in 514.

Now on 6 Referring now, a method of determining an offset in the VLA sensor when a vehicle is first assembled begins at 602. At 604, the method parks the vehicle on a surface with a predetermined slope. At 606, the method provides the predetermined surface slope to a powertrain control system (PCS) using, for example, a user interface device (UID) (eg, a touch screen) in the vehicle or an external module (eg, a scanning tool).

At 608, the method determines the sensor offset based on input from the VLA sensor and the predetermined tilt. For example, the method may estimate a longitudinal acceleration based on the predetermined grade and set the sensor offset equal to the difference between a longitudinal acceleration measured by the VLA sensor and the estimated longitudinal acceleration. The method ends in 610. The method may permanently store the sensor offset in non-volatile memory and adjust the sensor offset based on sensor offsets determined using other methods over the lifetime of the vehicle.

Now on 7 Referring to this, a method of determining the sensor offset begins at 702 each time the ignition key is turned off (eg, each time a vehicle ignition is cycled from on to off). or drive position) is switched to an off position. Alternatively, the method may determine if a button is depressed to toggle the vehicle ignition from on to off. The method proceeds to 706 if the ignition key is turned to the off position. Otherwise the ver proceed to determine in 704 whether the ignition key is turned to the off position.

At 706, the method saves the last reading from the VLA sensor prior to key-off. At 708, the method determines whether the ignition key is switched from the off position to the on (or drive) position. Alternatively, the method may determine if a button is depressed to toggle the vehicle ignition from off to on. If the ignition key is turned to the on position, the method proceeds to 710 . Otherwise, the method continues to determine in 708 whether the ignition key is turned to the on position.

At 710, the method obtains a new reading from the VLA sensor upon key-on (e.g., when the vehicle ignition is switched from off to on). At 712, the method determines the sensor offset based on the stored reading and the new reading. For example, the method may assume that the vehicle is in the same location when the ignition key is turned off and when the ignition key is turned on, and set the sensor offset equal to the difference between the stored reading and the new reading.

Now on 8th Referring to this, a method for determining the sensor offset over a relatively short trip (eg, a 16 to 48 km (10 to 30 mile) trip) begins at 802 the on (or drive) position is switched. Alternatively, the method may determine if a button is depressed to toggle the vehicle ignition from off to on. If the ignition key is turned to the on (or drive) position, the method proceeds to 806 . Otherwise, the method continues to determine in 804 whether the ignition key is switched from to the on (or drive) position.

At 806, the method takes an average of road grade estimates collected over a predetermined distance (e.g., 1 meter). In other words, the method estimates the road grade multiple times over the predetermined distance and then averages the road grade estimates collected over the predetermined distance. At 808, the method determines a running sum of averages of road grade estimates, where each of the averages corresponds to the predetermined distance. In other words, the method adjusts the running total at predetermined intervals of traveled distance each equal to the predetermined distance.

At 810, the method determines whether the ignition key is switched from the on (or drive) position to the off position. Alternatively, the method may determine if a button is depressed to toggle the vehicle ignition from on to off. If the ignition key is turned to the off position, the method continues to 812 . Otherwise, the method continues at 810 to determine whether the ignition key is switched from the on (or drive) position to the off position.

At 812, the method determines whether the sum of the averages corresponds to a round trip. The method may be performed using the methods described above with respect to the sensor offset determination module 206 of FIG 2 carried out criteria determine whether the total corresponds to a round trip. If the sum corresponds to a round trip, the method continues to 814 and determines the sensor offset based on a difference between the sum and zero. Then, in 816, the method resets the sum to zero. If the sum does not correspond to a round trip, the method continues at 816 and resets the sum to zero without determining the sensor offset based on the sum at 814 .

Before determining whether the total corresponds to a round trip, the method may determine whether the distance traveled since the total was last reset is sufficient to make such a determination. For example, the distance traveled may be greater than or equal to a daily commute distance. If the distance traveled is sufficient, the method can proceed to determine if the total is a round trip. Otherwise, the method can continue to find the sum of the means.

Now on 9 Referring, a first method of determining a sensor offset due to vehicle aging and a variation in the VLA sensor output over the life of the vehicle begins at 902. At 904, the method generates a histogram of road grade estimates, such as the histogram 302 from 3A , and it performs this. The road grade estimates can be grouped into classes having smaller magnitudes around 0% grade and larger magnitudes at steeper grades.

At 906, the method determines whether the distance traveled by the vehicle since the histogram was generated (e.g., since the data in the histogram was last cleared) is greater than or equal to a predetermined distance (e.g., 1,600 kilometers (1,000 miles)) is. If the distance traveled is greater than or equal to the predetermined distance, the method continues to 908 . Otherwise, the method continues at 904 to maintain the histogram.

At 908, the method determines whether a sum of all classes is outside of a predetermined range. If the sum of all classes is outside of the predetermined range, the method continues at 910 and determines the sensor offset based on an amount that the sum is outside of the predetermined range. The method then continues in 912 and clears all data in the histogram. If the sum of all classes is within the predetermined range, the method continues in 912 and clears all data in the histogram without determining the sensor offset based on the histogram.

The predetermined area may be an area centered around a 0% road grade (e.g. +/- 0.278%). The predetermined range may correspond to a worst case error in this method. Worst-case error may correspond to driving the vehicle 19,312 kilometers (12,000 miles) per year from a lowest possible terrain elevation (e.g., -86 meters (-282 feet)) to a highest possible terrain elevation (e.g., 4,401 meters (14,440 feet)).

Now on 10 Referring to this, a second method for determining a sensor offset due to vehicle aging and a variation in the output of the VLA sensor over the life of the vehicle begins at 1002. At 1004, the method determines a running sum based on changes in an altitude of the vehicle on the estimated road grade. The method can find the sum of the elevation changes using relationship (5) as explained above.

At 1006, the method determines whether the distance traveled by the vehicle since the sum was reset to zero is greater than or equal to a predetermined distance (e.g., 1,600 kilometers (1,000 miles)). If the distance traveled is greater than or equal to the predetermined distance, the method continues at 1008 . Otherwise, the method continues at 1004 to determine the sum of the elevation changes.

At 1008, the method determines whether the sum of elevation changes is outside of a predetermined range. If the sum of the elevation changes is outside of the predetermined range, the method continues at 1010 and determines the sensor offset based on an amount that the sum is outside of the predetermined range. The method then continues at 1012 and resets the sum to zero. If the sum of the elevation changes is within the predetermined range, the method continues at 1012 and resets the sum to zero without determining the sensor offset based on the sum.

The predetermined area may be an area centered around a 0% road grade (e.g. +/- 0.278%). The predetermined range may correspond to a worst case error in this method. Worst-case error may correspond to driving the vehicle 19,312 kilometers (12,000 miles) per year from a lowest possible terrain elevation (e.g., -86 meters (-282 feet)) to a highest possible terrain elevation (e.g., 4,401 meters (14,440 feet)).

Now on 11 Referring to this, a method for determining the sensor offset when servicing the vehicle begins at 1102. At 1104, the method parks the vehicle at a location with the vehicle facing in a first direction. At 1106, the method obtains a first estimate of the road grade based on the output from the VLA sensor. At 1108, the method parks the vehicle at the same location with the vehicle facing in a second direction, opposite the first direction.

At 1110, the method obtains a second estimate of the road grade based on the output from the VLA sensor. At 1112, the method determines the sensor offset based on the first and second estimates. The method may determine the sensor offset based on the first and second estimates as described above with respect to the sensor offset determination module 206 of FIG 2 determine explained. The procedure ends in 1114.

Claims (8)

A method comprising: estimating a longitudinal acceleration of a vehicle (400) based on at least one of a transmission output speed and a wheel speed; the longitudinal acceleration of the vehicle (400) is measured; an offset in the measured longitudinal acceleration is determined; estimating a grade of a road on which the vehicle (400) is traveling based on the estimated longitudinal acceleration, the measured longitudinal acceleration, and the offset; and an actuator (102) of the vehicle (400) based on the estimated road grade is controlled; characterized in that the offset is determined based on a first road grade estimated when the vehicle (400) is parked at a location while facing in a first direction and a second road grade estimated when the vehicle (400) is parked in the same location and facing in a second direction opposite to the first direction. procedure after claim 1 , further comprising estimating the road grade based on a difference between the measured longitudinal acceleration and a sum of the estimated longitudinal acceleration and the offset. procedure after claim 1 , further comprising that when the vehicle (400) is parked on a surface with a predetermined slope, the offset is determined based on the measured longitudinal acceleration and the predetermined slope. procedure after claim 1 The further comprising: storing a first value of longitudinal acceleration measured when an ignition system (119) of the vehicle (400) is switched from on to off; receiving a second value of longitudinal acceleration measured when the ignition system (119) is switched from off to on; and the offset is determined based on a difference between the first and second values. procedure after claim 1 , further comprising: determining a sum of averages of the estimated road grade over a predetermined distance; and the offset is determined based on a difference between the sum and zero when the sum corresponds to a round trip. procedure after claim 1 , further comprising: maintaining a histogram by grouping multiple values of estimated road grade into bins; and the offset is determined based on an extent to which a sum of the classes falls outside of a predetermined range. procedure after claim 1 The further comprising: determining changes in a height of the vehicle (400) at first predetermined intervals of a distance traveled by the vehicle (400) based on the measured longitudinal acceleration; determining a sum of elevation changes at second predetermined intervals of a distance traveled by the vehicle (400); and determining the offset based on an amount by which the sum of the elevation changes is outside a predetermined range. procedure after claim 7 , further comprising the offset being further based on: a vehicle height estimated based on an ambient barometric pressure; and/or a lowest possible terrain elevation; and/or a highest possible terrain height is determined.

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